Caught in the Act!

• Heidi Klum, saying “Auf Wiedersehen” to any holiday weight with a vigorous training session at Fitness Factory in West Hollywood. The Project Runway host hit the treadmill, lifted weights and worked up a noticeable sweat with her personal trainer Witold Szmanda. “She was pumped up going in, and that wasn’t an easy workout,” an onlooker says. “She was smiling and laughing the entire time.”

• While in Miami for teammate Nick Swisher‘s wedding toJoanna Garcia, Alex Rodriguez and Cameron Diaz enjoyed lunch at the Soho House, then a romantic dinner at Prime 112. The two entered the restaurant together and immediately headed into a private wine room for dinner, where they ate with the curtains drawn. But an onlooker tells us, “At one point, Alex actually reached over and kissed her.” And the whole restaurant “stopped and watched,” the onlooker adds.

• True Blood hottie Ryan Kwanten, practicing yoga at Yoga Works on Main Street in Venice, Calif., in skintight Under Armour athletic gear. And the TV star was a hands-on participant: He helped his neighbor achieve the perfect headstand.

• Paris Hilton, partying at Sammy Hagar’s Cabo Wabo Cantina inside Las Vegas’s Planet Hollywood Resort & Casino. The heiress was there with three friends, and they enjoyed some frozen daiquiris. The ladies were also chatting about Hilton’s new reality show.

• Katy Perry and Russell Brand, who tied the knot in India, giving travel tips and recommendations of places to stay to Ed Norton at the Change Begins Within event in N.Y.C.